Transducer and systems for high speed measurement of shock loads

Abstract

A transducer and system for optically indicating the level of stress experienced during loading. The system is designed for use in shock loading conditions. The transducer uses a transducer piece made from a crystalline luminescent material such as ruby. The transducer piece is preferably positioned between one or two support pieces, preferably along flat faces to create a uniform stress field within a limited detection area. The system uses the luminescent output from the detection area to produce a spectral output with time using a spectrometer and streak camera. The streak camera output is advantageously converted to digital signals for storage and analysis.

We claim: 
     
       1. An optical stress transducer for use in measuring high stresses applied at high loading rates with a time resolution of at least one microsecond, and having the ability to discern stress from nonhydrostatically applied loads, the transducer comprising: a transducer piece made of a luminescent crystalline material that exhibits a frequency shift in luminescent output as a function of stress, the transducer piece substantially comprising a single crystal within a detection area, said transducer piece being specifically positioned in a known orientation relative to the direction of at least one applied force; the transducer piece having first and second faces which are substantially flat and parallel and adapted to receive applied force, the faces being separated by a thickness dimension which is substantially uniform over the faces of the transducer piece; the transducer piece also having at least one minimum lateral dimension which defines a minimum width across the faces of the transducer piece; said minimum lateral dimension being sufficient so that a strain rarefaction wave which propagates inwardly from an outer edge of the transducer piece during high stress conditions, does not reach the detection area of the transducer piece within a time period sufficient for information indicating stress to be detected from said detection area;   a first support piece having an inner face which is substantially flat and engages the transducer piece to apply an approximately uniform stress over the first face of the transducer piece; and   a second support piece having an inner face which is substantially flat and engages the transducer piece to apply an approximately uniform stress over the second face of the transducer piece.   
     
     
       2. The optical stress transducer of claim 1 wherein the first and second support pieces each have outer faces which are substantially flat and parallel to said transducer piece faces. 
     
     
       3. The optical stress transducer of claim 1 further comprising means for beaming a stimulating beam of laser light onto said detection area of the transducer piece. 
     
     
       4. The optical stress transducer of claim 3 wherein said means for beaming includes an optical fiber. 
     
     
       5. The optical stress transducer of claim 4 further comprising: lens means interposed between an end of the optical fiber and an outer face of the first support piece for focusing laser light onto said detection area of the transducer piece.   
     
     
       6. The optical stress transducer of claim 4 wherein said optical fiber extends through an aperture in one of said support pieces adjacent to said detection area. 
     
     
       7. The optical stress transducer of claim 1 wherein the minimum lateral dimension is at least three times said thickness dimension. 
     
     
       8. The optical stress transducer of claim 1 further comprising retaining means for retaining said transducer piece and said first and second support pieces in an assembly. 
     
     
       9. The optical stress transducer of claim 8 wherein the retaining means is adjustable for enabling precise alignment of the transducer piece relative to a direction of applied force. 
     
     
       10. The optical stress transducer of claim 1 wherein the transducer piece is disk shaped. 
     
     
       11. The optical stress transducer of claim 10 wherein the first and second support pieces are disk shaped. 
     
     
       12. The optical stress transducer of claim 1 wherein the transducer piece and the first and second support pieces are assembled together with the inner faces of the first and second support pieces being adjacent to the first and second faces of the transducer piece, respectively. 
     
     
       13. The optical stress transducer of claim 12 wherein the transducer piece and the support pieces are disk shaped with the inner faces of the support pieces being at least as large as the faces of the transducer piece. 
     
     
       14. The optical stress transducer of claim 13 wherein the detection area is located about a central axis of the disk-shaped transducer piece, and wherein the minimum lateral dimension is at least three times said thickness dimension. 
     
     
       15. The optical stress transducer of claim 1 wherein a principal crystallographic axis of the single crystal within the detection area is oriented normal to the first and second faces of the transducer piece. 
     
     
       16. The optical stress transducer of claim 15 wherein the single crystal is Z-cut and the C-axis of the crystal is orthogonal to the first and second faces of the transducer piece. 
     
     
       17. The optical stress transducer of claim 1 further comprising: a backup disk positioned against an outer surface of the first support piece.   
     
     
       18. An optical stress transducer for use in measuring high stresses applied at high loading rates with a time resolution of at least one microsecond, and having the ability to discern stress from nonhydrostatically applied loads, the transducer comprising: a transducer piece made of a luminescent crystalline material that exhibits a frequency shift in luminescent output as a function of stress, the transducer piece substantially comprising a single crystal within a detection area, said transducer piece being specifically positioned in a predetermined orientation relative to the direction of at least one applied force; the transducer piece having first and second faces which are substantially flat and parallel and adapted to receive applied force, the faces being separated by a thickness dimension which is substantially uniform over the faces of the transducer piece; the transducer piece also having at least one minimum lateral dimension which defines a minimum width across the faces of the transducer piece; said minimum lateral dimension being sufficient so that a strain rarefaction wave which propagates inwardly from an outer edge of the transducer piece during high stress conditions, does not reach the detection area of the transducer piece within a time period sufficient for information indicating stress to be detected from said detection area; and   a first support piece having an inner face which is substantially flat and engages the transducer piece to apply an approximately uniform stress over the first face of the transducer piece.   
     
     
       19. The optical stress transducer of claim 18 wherein the first support piece has an outer face which is substantially flat and parallel to said transducer piece faces. 
     
     
       20. The optical stress transducer of claim 18 wherein the minimum lateral dimension is at least three times said thickness dimension. 
     
     
       21. The optical stress transducer of claim 18 wherein the transducer piece and the first support piece are assembled together with the inner face of the first support piece being adjacent to the first face of the transducer piece. 
     
     
       22. The optical stress transducer of claim 18 wherein a principal crystallographic axis of the single crystal within the detection area is oriented normal to the first and second faces of the transducer piece. 
     
     
       23. The optical stress transducer of claim 18 wherein the single crystal is Z-cut and the C-axis of the crystal is orthogonal to the first and second faces of the transducer piece. 
     
     
       24. The optical stress transducer of claim 18 further comprising retaining means for retaining said transducer piece and said first support piece in an assembly. 
     
     
       25. The optical stress transducer of claim 24 wherein the retaining means is adjustable for enabling precise alignment of the transducer piece relative to a direction of applied force. 
     
     
       26. A system for use in measuring high stresses applied at high loading rates with a time resolution of at least one microsecond, and having the ability to discern stress from nonhydrostatically applied loads, the system comprising: an optical stress transducer comprising:   a transducer piece made of a luminescent crystalline material that exhibits a frequency shift in luminescent output as a function of stress, the transducer piece substantially comprising a single crystal within a detection area, said transducer piece being specifically positioned in a predetermined orientation relative to the direction of at least one applied force; the transducer piece having first and second faces which are substantially flat and parallel and adapted to receive applied force, the faces being separated by a thickness dimension which is substantially uniform over the faces of the transducer piece; the transducer piece also having at least one minimum lateral dimension which defines a minimum width across the faces of the transducer piece; said minimum lateral dimension being sufficient so that a strain rarefaction wave which propagates inwardly from an outer edge of the transducer piece during high stress conditions, does not reach the detection area of the transducer piece within a time period sufficient for information indicating stress to be detected from said detection area; and   a first support piece having an inner face which is substantially flat and engages the transducer piece to apply an approximately uniform stress over the first face of the transducer piece;   a laser light source in optical communication with the detection area of the transducer piece to excite the detection area into a luminescent discharge;   beam splitting means for separating incident laser light and luminescent discharge from the detection area;   spectrometer means for spectrally dispersing the separated luminescent discharge; and   high speed time resolving recording means for recording the spectrally dispersed luminescent discharge with a time resolution of at least one microsecond.   
     
     
       27. The optical stress transducer of claim 26 wherein the high speed time resolving recording means has a time resolution of at least 100 nanoseconds or faster. 
     
     
       28. The optical stress transducer of claim 26 wherein the high speed time resolving recording means has a time resolution of at least 50 nanoseconds or faster. 
     
     
       29. The optical stress transducer of claim 26 wherein the first support piece has an outer face which is substantially flat and parallel to said transducer faces. 
     
     
       30. The optical stress transducer of claim 26 wherein the minimum lateral dimension is at least three times said thickness dimension. 
     
     
       31. The optical stress transducer of claim 26 wherein the transducer piece and the first support piece are assembled together with the inner face of the first support piece being adjacent to the first face of the transducer piece. 
     
     
       32. The optical stress transducer of claim 26 wherein a principal crystallographic axis of the single crystal within the detection area is oriented normal to the first and second faces of the transducer piece. 
     
     
       33. The optical stress transducer of claim 26 wherein the single crystal is Z-cut and the C-axis of the crystal is orthogonal to the first and second faces of the transducer piece. 
     
     
       34. The optical stress transducer of claim 26 further comprising retaining means for retaining said transducer piece and said first support piece in an assembly. 
     
     
       35. The optical stress transducer of claim 34 wherein the retaining means is adjustable for enabling precise alignment of the transducer piece relative to an applied force. 
     
     
       36. The optical stress transducer of claim 26 wherein the laser light source is beamed through a focusing means to minimize the detection area stimulated by the laser light source. 
     
     
       37. A method for measuring high stresses applied at high loading rates by at least one applied force loading, comprising: obtaining a transducer piece having opposing, substantially flat and parallel first and second faces; said transducer piece being made from a crystalline luminescent material which exhibits a frequency shift in luminescent output as a function of stress;   selecting a detection portion of said transducer piece which comprises substantially a single crystal structure; said detection portion of said transducer piece being sufficiently spaced inwardly from outer edges of the transducer piece so that a strain rarefaction wave generated from said outer edges during stressed conditions does not reach the detection portion within a time period sufficient for information indicating stress to be detected from said detection portion;   supporting the transducer piece between first and second support pieces having flat inner surfaces which bear on said first and second faces of the transducer piece;   positioning the transducer piece in a predetermined orientation with respect to a direction of at least one applied force loading;   stimulating the detection portion of the transducer piece with an appropriate optical beam so as to cause luminescent emissions to occur therefrom;   stressing the transducer piece by subjecting it to stressed conditions throughout the detection portion;   measuring the frequency of luminescent emissions occurring from the detection portion at least once during unstressed conditions and at least once during stressed conditions and prior to inpingement of said strain rarefaction wave upon said detection portion; and   comparing differences in the luminescent emissions occurring during unstressed conditions and stressed conditions to achieve an indication of the stressed conditions existing in the transducer piece when the measuring step was performed.